Correlating to runs scored, Dan Fox puts RC formulas at .958 (simple) and .964 (current, more complicated Bill James formula). Just to make clear (I know you know this already) the abve values are r^2 values, not "percentage within", which Al brought up earlier. Here's an example of a full season. Does this formula get more accurate with large samples? Run estimators use aggregate stats, so context is largely stripped out (diff estimators do this diff ways). For instance, a linear weights approach would say that a HR is worth 1.4 runs, with the .4 part coming from an average number of base runners on during those home runs. Well, if a team has a very high OBP, a HR is actually worth more since there will be, on average, more base runners on. What about a big HR hitter in the 8th spot? He'll probably have less base runners than would be expected by looking only at team OBP (as basic RC and others do). As you use a larger and larger sample, these peculiarities begin to cancel each other out, making the results become more and more accurate. As a general rule of statistical analysis, larger sample sizes result in greater accuracy for this very reason. Individual data has random uncertainty that should average toward the actual value. Russ, you've mentioned (very minor) flaws with using OBP times SLG times AB. Can you refresh our memories? Well, all run estimators are "flawed" by default, since they try to model the results of chain of probabalistic events with aggregate data. Unless you are using a simulator Markov Chain analysis, you are using a very simplified (essentially flawed) scoring model. Some are simply less flawed than others. Now how to measure "accurate" or "flawed" is subjective anyway. Dan Fox covers this in the below article: A Closer Look at Run Estimation No matter how advanced a run estimator is, it will never be perfect. Even if you know Lee is going to hit 45 home runs, no one can predict exactly WHEN he will and what the exact context will be when he does. Sorry for the long rambling post.